The proposed studies are based on the hypothesis that allograft rejection is an antigen-dependent, destructive inflammatory process that is superimposed on the repair-oriented inflammatory process that occurs in both the isograft and allograft. Both grafts acquire an inflammatory cellular infiltrate, but the signals that initiate allograft inflammation are not known. Acute rejection, even when reversed, is associated with decreased graft survival, and the identification and inhibition of very early events in graft rejection should be of significant therapeutic value. We will study early cytokine expression by T lymphocyte subsets and the expression of antigen-dependent and antigen-independent inflammatory adhesion molecules by endothelia in rejecting murine cardiac allografts and relate them to the presence of allogeneic class I or class II MHC. Specifically, we will 1) analyze cytokine expression in T cells and endothelial cells and cell surface phenotype in endothelial cells from rejecting cardiac allografts. We will use PCR, immunohistochemistry and ELISPOT analysis of T cells and endothelial cells isolated by cell sorting to establish a baseline of cytokine synthesis and expression of endothelial cell surface molecules during early allograft inflammation. 2) determine the respective contributions of CD4+ and CD8+ T lymphocytes to cytokine expression in the graft. We will separate T cells into CD4+ and CD8+ subsets to determine whether they contribute different cytokines to the alloresponse, and whether they are recruited into the response with different kinetics. 3) determine the effect of single MHC disparity on the activity of CD4+ and CD8+ cells in the development of allograft inflammation. We will perturb the allograft system by disallowing immune activation via class I or class II MHC, and examine the effects on the recruitment of CD4+ and CD8+ cells into the inflammatory response, early cytokine synthesis, and expression of inflammatory adhesion molecules by graft endothelia. 4) determine the effects of interference with in vivo CD4+ and CD8+ cell function on allograft inflammation in class I and class II disparate grafts. We will use antibodies to CD4, CD8 and IFNgamma to remove or inhibit the function of CD4+ and CD8+ cells in class I or class II disparate grafts. In effect, we will dissect the in vivo allograft response to determine the role of CD4+ and CD8+ cells in the development of antigen-dependent destructive inflammation. In general, these studies will demonstrate the role of T lymphocyte subsets in establishing the cytokine environment of the allo-response in vivo. In so doing, they will provide new information regarding early events in allograft inflammation.